In the solution ring opening polymerization of cycloolefins, the product discharged from the reactor is a honey-like cement that consists principally of a nonpolar carrier solvent in which the polymer is dissolved. The polymer content is normally on the order of about 15% by weight. The polymer can be any of the family of polymers that are made by homopolymerization or copolymerization of one or more of cycloolefins that contain the norbornene group. Polymerization can be conducted batchwise or continuously.
After the honey-like cement is prepared, it is necessary to separate the polymer from its carrier solvent. In the past, steam stripping has been used exclusively in plant operations to extract the polymer from the carrier solvent. In steam stripping, the cement is injected into a jet of steam that is directed into a vessel containing hot water. As contact is made between the cement and steam, the carrier solvent is flashed off as vapor, depositing the polymer in particle form in the hot water.
Steam stripping has a number of serious disadvantages. It produces a product of relatively large, coarse and variable particle size. The product contains a substantial amount of occluded water that makes it extremely difficult to dry. It produces a product that retains significant quantities of residual monomers and other impurities, all of which adversely affect the quality of the final product. Steam stripping has the inherent carry-over problem of polymer fines when the solvent vapor is discharged. This carry-over results in severe plugging in the solvent recovery system. Finally, stream stripping requires large volumes of steam, far in excess of that required to vaporize the solvent in order to produce a particulate product. Steam stripping, therefore, is an inefficient, expensive, and energy-wasteful operation.
It has been a common practice to reduce impurities in the polymers of cycloolefins by water washing the cements before steam stripping. In this way, effects of certain water-sensitive impurities are eliminated. Water washing has not been practical since large volumes of contaminated water were produced that had to be disposed without creating an environmental problem.
More recently, an alternate approach was discovered for isolating polymers of cycloolefins from the carrier solvent. Pursuant to this approach, the cement is mixed in a high shear mixer with a nonsolvent in the volume ratio of about 3 to 1 nonsolvent to cement whereby the polymer precipitates out. A nonsolvent is a liquid that is miscible with the nonpolar solvent that is used in the polymerization reaction but is a nonsolvent for the polymer. Examples of suitable nonsolvents include, ethanol, propanol, isopropanol, and the like, and they can be used with or without water. Although on some occasions this recovery procedure produced granular, easy-to-dry product having bulk density of about 0.144 g/cc or 9 lb/ft.sup.3, these results could not be reliably reproduced. What was obtained normally was a clump-like product of fine, irregular fluffy microfibers that packed cotton-like when filtered and was difficult to dry and handle. The dry product normally had a bulk density below 0.08 g/cc or 5 lb/ft.sup.3.
In a related patent application entitled "Precipitation of Polymeric Cycloolefins" by inventors Messrs. G. V. Wootton and L. P. Tenney, filed May 10, 1982 and bearing Ser. No. 376,367 an invention is disclosed which also relies on the use of a nonsolvent alcohol and water for precipitation of polycycloolefins. However, in that application, amount of water used relative to the nonsolvent alcohol generally corresponds to the azeotropic composition of water and the alcohol which facilitates recovery operations by making it possible to boil off the azeotrope.